I've also edited the yearbook service report for analysis below. I've eliminated all columns except 2 columns - the 2015 and 2014 Average publishers. I've sorted from largest to smallest based on the column "A subtract B".

Overall the report shows stagnation. There are still plenty of people enthusiastically making the WT their life's work that it will be around for a long while yet, but many are just finding it boring. When a country gets to the point where there are nearly as many ex-witnesses as current witnesses, the growth stops. That would be an interesting figure to have, it if were possible to get.